1. Field of the Invention
The present invention is related to a linear actuator.
2. Description of the Related Art
A linear actuator converts a rotational motion into a linear motion. For example, Japanese Patent Laid-Open. No. H11(1999)-264451 introduced a linear actuator, which converts the rotational motion of a motor mounted on the main body into the linear motion by a power transmission mechanism which comprises a feed screw unit driven in rotation via the motor and a feed nut unit screwed to the feed screw unit, thereby moving linearly the actuation member in the axial direction of the feed screw unit. In addition, Japanese Patent Laid-Open No. 2002-58271 disclosed a linear servo actuator capable of detecting the position of a slider with high accuracy.
To this end, the linear servo actuator comprises a magnetostriction potentiometer for detecting the position of a slider, and a position control unit in charge of feed back control of the position of the slider based on the difference between the position of the slider and a command position.
However, these conventional techniques have the following problems.
For instance, the linear actuator disclosed in Japanese Patent Laid-Open No. H11(1999)-264451 is not equipped with a position sensor for detecting the position of an actuation member. Thus, to execute the positioning of the actuation member, a sensor has to be installed additionally.
On the other hand, the linear servo actuator disclosed in Japanese Patent Laid-Open No. 2002-58271 is equipped with a magnetostriction potentiometer as a position sensor for detecting the position of the slider. The magnetostriction potentiometer comprises a magnetostriction scale and a magnetostriction head. Since the magnetostriction scale was mounted on a platen which is a fixed member and the magnetostriction head on the slider formed movably on the platen, the overall actuator size became too large. In addition, an expensive linear pulse motor implemented as a driving motor increased the price of the actuator.